The Chiltern Hills in England are made from what type of rock?

The Chiltern Hills or, as they are known locally and historically, the Chilterns, is a range of hills northwest of London. They form a chalk escarpment across Oxfordshire, Buckinghamshire, Hertfordshire, and Bedfordshire. A large portion of the hills was designated officially as an Area of Outstanding Natural Beauty in 1965.

The Chilterns cover an area of 322 square miles (830 km2) stretching 45 miles (72 km) in a southwest to a northeast diagonal from Goring-on-Thames, Oxfordshire to Hitchin, Hertfordshire. At their widest, they are 12 miles (19 km).

The chalk escarpment of the Chiltern Hills overlooks the Vale of Aylesbury, and roughly coincides with the southernmost extent of the ice sheet during the Anglian glacial maximum. The Chilterns are part of a system of chalk downlands throughout eastern and southern England, formed between 65 and 95 million years ago, comprising rocks of the Chalk Group; this also includes Salisbury Plain, Cranborne Chase, the Isle of Wight and the South Downs in the south.